Retirement Benefits and Trusteed Assets (OPEB - Postretirement Cost Inclusions) (Details) (Other Postretirement Benefit Plan [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	$ 26	$ 35	$ 51
Interest cost	68	67	91
Expected return on plan assets	(85)	(74)	(61)
Amortization of net loss	14	47	58
Amortization of prior service cost (credit)	(109)	(100)	(14)
Net pension cost	$ (86)	$ (25)	$ 125